I've been trying to setup Review Board on a Windows Vista box and had the same problem. Indeed, rebuilding PyCrypto with MinGW solves the problem.
As to the build problem, you probably meant a missing chown.exe tool error. It seems that you don't have MSYS installed (it's an optional part of MinGW that isn't installed by default). I guess the problem would disappear if you re-installed MinGW and chosen all the components but I simply downloaded the missing packages from the command line by (I'm not sure but think these were the only two):
mingw-get install msys-base
mingw-get install msys-sed
One more problem I ran into was that "-mno-cygwin" compiler switch is pushed into GCC by distutils (setup.py install script) while it's not supported any longer by GCC 4, which is distributed as a part of MinGW. I read that you might customise the compiler switches used by the python extension build process using a sort of a script but it turned out I have GCC 3 (that supports -mno-cygwin) as a part of ActivePerl so I modified the Path environment variable to have a path to Perl before a path to MinGW to force GCC 3 to be used. There might be a better way to fix the problem but it did the job.
Hope that helps.

We *strongly* encourage you to install in Linux, possibly in a virtual machine. Windows support is minimal and we actively encourage you to move away from it. We may even have to face the reality of dropping support in the future, as many of the libraries we depend on are not tested on Windows.

As the error message suggests ("C:\MinGW\bin\gcc.exe") you're still somehow using MinGW version of GCC. The only thing I might suggest is double-checking that there're no typos in you Path. Also, make sure you really have GCC in your perl\bin. It might be that GCC gets there with one of the additional packages (I use Perl from time to time so I probably have a few of them) rather than the base installation.
I must stress that what I did was a clumsy (but quick for me) workaround rather than a real solution. If you really want to follow in my footsteps you might try running the perl package manager ('ppm' command that starts a small gui app) and look for mingw package (a barebones one: gcc+dmake and not much more) as it seems that Perl relies on the "legacy" GCC 3. I'm not sure but it *might* work. Google says 'ppm install MinGW' from the command line should do the job but I would run ppm gui app to make sure that there aren't more than one version of this package.
An alternative (and maybe better) solution could be to fix distutils Python module that unnecessarily adds this compiler switch. If you do a full text search for 'mno-cygwin' in the Python install directory you might even find a script that adds it but I haven't tried patching it.
Another option, MinGW itself has some legacy packages available but using them is slightly more involved because you need to be carefull not to mix and match the new and old ones e.g. http://mingw-users.1079350.n2.nabble.com/How-do-I-install-mingw-gcc-3-4-5-td5604746.html.

Congratulations. I though you've given up.
In the meantime, I've finished evaluating Review Board (I really like it) and I've decided to try and introduce it to the team I work with in my organization. I didn't want to risk (now or in the future) all these compatibility problems with dependent components and installed it on our Linux intranet server. As chip...@gmail.com said, it's so much simpler... I didn't have any problems, depite having moderate at most knowledge of unix-like systems.

wojciech...@gmail.com
Thanks for your help to make me install it on windows successfully!
Is it possible to share your evaluation resources and result to me? We only have a small team (<10 people), and I want to make the whole development process more automated and agile.
my email:brucenan@gmail.com
We also can have more communication about RB.